1. Field of the Invention
The present invention relates generally to detecting the level of a liquid and, more particularly, is concerned with apparatus for determining when the level of a liquid reaches a predetermined value and apparatus for measuring the level of a liquid.
2. Description of the Prior Art
An operational step in the nuclear fuel fabrication process is the pickling operation for nuclear fuel rod cladding tubes to size and clean the zirconium tubes' inside surface before such tubes are loaded with nuclear fuel pellets. For this operation, the tubes are placed in an acid-filled tank. The nitric and hydrofluoric acid pickling solution is kept hot by submerged electric heaters. The heaters must be turned off if they are exposed to air, such as through evaporation or draining of the pickling solution. In practice, heaters have been destroyed through overheating when inadvertently left energized with the acid removed from the tank.
Commercially available liquid level detectors have been used to monitor the fluid level around the heaters. These detectors were used to shut off the heaters and/or refill the tank when a low liquid level was encountered. However, these detectors had a short life span in the harsh environment of the acid pickling solution with the detectors being repeatedly cycled on and off in the turbulent liquid encountered when a batch of tubes was placed into, or removed from, the acid. It was felt these detectors failed from the repeated cycling rather than from the acid. Such detectors included a float mechanically connected to a switch and a float having a magnet which activates a sealed magnetic reed switch.
What is needed is an economical liquid level detector which can operate in a harsh environment, one which is resistant to acid and one which can withstand repeated on-off cycling under wave action.